High temperature resistor



April 1961 A. o. LIERMANN ETAL 2,980,877

HIGH TEMPERATURE RESISTOR Filed Sept. 13, 1957 FIG.3

INVENTQRSI AUGUST 0. LlERMANN, CHARLES W. HEATH THEIR ATTORNEY.

United States Patent HIGH TEMPERATURE RESISTOR August '0. Liermann and Charles W. Heath, Auburn,

N.Y., assignors to General Electric Company, a corporation of New York Filed Sept. 13, 1951, Ser. No. 683,751

4 Claims. c1. ass-25s The present invention relates to the construction of new and improved electrical components for operation at high temperatures.

More particularly, the invention relates to a new and improved terminal construction for resistors capable of operating in ambient temperatures of 500 C. or better.

With the advent of high temperature resistors for use in constructing electronic equipment capable of operating in ambient temperatures of 500 C. or better, the problem of making reliable electrical connections to such resistors has become of considerable importance. Conventional methods for securing terminal leads to resistors for operation in the higher temperature ranges utilize such techniques as spotwelding, butt-welding or brazing. It has been determined that under the rigors of high temperature use, such conventional means for making connections to resistors have not proven too reliable.

"It is therefore a primary object of the present invention to provide a new and improved terminal construction for connecting the lead in terminals to resistors capable of operating in ambient temperatures of 500 C. or better.

In practicing the invention a new and improved resistor is provided which comprises a hollow open ended ceramic body exhibiting a predetermined electrical resistance between its ends. Metal end caps are secured to the open ends of the ceramic body by a ceramicmetal eutectic seal for hermetically sealing closed the hollow interior of the ceramic body. Metal leads for connecting the resistor in electrical circuit relationship are then secured to the resistor by means of the metal leads caps formed from a metal similar to the metal of the end caps but difierent from the metal of the leads. The lead caps have an embossment therein for receiving the ends of the leads, and serve to secure the leads over the end caps in electrical conductive relationship by a metal to metal eutectic bond.

Other objects, features, and many of the attendant advantages of this invention will become better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein, like parts in each of the several figures are identified by the same reference character, and wherein:

Fig. 1 is a sideelevation view of a high temperature resistor constructed in accordance with the present invention;

Fig. 2 is an exploded perspective view of the resistor shown in Fig. 1;

Fig. 3 is a partial sectional view of an alternative form of a new and improved terminal construction used on the resistor shown in Figs. 1 and 2; and

Fig. 4 is still a different form of a new and improved terminal construction for the high temperature electrical ice comprises a high temperature resistor formed by a hollow cylindrical open ended ceramic body 11. The ceramic body 11 preferably comprises alumina, but could be formed of other ceramic materials having desired high temperature qualities such as forsterite or steatite. On the interior surface of the hollow ceramic body 11 is an electrically conductive, high resistance film or layer exhibiting a desired electrical resistance between the ends thereof and formed in any suitable manner such, for example, that described in commonly assigned application Serial No. 464,080, Conducting Films, J. E. Beggs, filed October 22, 1954.

[he hollow open ended ceramic cylinder 11 is closed by a pair of metal end caps 12 each of which comprises a pair of laminated metal discs 13 and 14. The disc 13 preferably comprises titanium, but may also comprise some other suitable metal having a high melting temperature such as zirconium, hafnium, thorium, tantalum or alloys thereof. The disc 14 preferably comprises nickel, but may also comprise either iron, cobalt, copper, chromium, molybdenum, platinum or alloys thereof. Discs 13 and 14 maybe pre-punched and subsequently bonded together by a suitable adhesive to facilitate their handling in further stages of .the assembly operation, or sheets of such metals may be adhesively bonded together first, and the disc-shaped end caps 12 and lead caps 16 subsequently punched out there-- from.

The high temperature resistor shown in Figs'l and 2 is completed by leads 15 which are attached over each of the open ends of ceramic body 11, and are preferably formed fromplatinum Wire, platinum coated titanium wire or platinum coated tantalum wire. The leads 15 are secured over end caps 12 by means of lead caps 16. The lead caps 16 are formed by a pair of laminated discs 17 and 18 in precisely the same manner as were the end caps 12, and are constructed from the same materials. The lead caps 16 differ from end caps 12 however, in that an embossed groove 19 is formed therein for receiving and seating the leads 15. While both of the metal discs 17 and 18 which comprise the laminated lead caps 12 are shown to be embossed, it is of course possible to have only disc 17 embossed to receive and seat the leads 15.

After completion of the fabrication of the component parts of the high temperature resistor illustrated in Figs. 1 and 2, the parts are assembled together to form the completed resistor. This is done by placing the embossed lead caps 16 plus the wire leads 15 on top of the end caps 12 which are in turn placed over the open ends of the cylindrically shaped hollow ceramic body 11. It is of course understood that the resistive film previously has been sprayed or otherwise formed on the interior surface of the hollow ceramic body 11. The assembled parts are then placed in a suitable holding fixture for heating, or if desired, temporary spot-welding or adhesive bonding of the assembled parts may be used to facilitate handling the same. The assembled structure is then placed in a vacuum furnace and fired to the melting point of the electric alloy until a eutectic liquidus is formed. In the case of the preferred embodiment employing tantalum and nickel disks, the structure may be fired to a temperature in the neighborhood of 1050? centigrade in a vacuum of less than one micron, for example. This firing operation causes the faces of the laminate discs comprising each of the end caps 12 and lead caps 16 to melt and form a metal-to-metal eutectic bond between the end caps, lead wires 15, and the lead caps, and, simultaneously, to form a ceramic-metal seal between the ceramic body 11 and end caps 12. For a more detailed description of the manner in which the eutectic bond is formed, reference is made to commonly Patented Apr. 18, 1961- assigned United States patent application Serial No. 409,159, entitled Metallic Bond, J. Beggs, inventor, filed February 9, 1954, now U.S. Patent 2,857,663. After firing, the resistor body is allowed to cool to room temperature, and thereafter the resistor may be assembled together with other electrical components for use in electronic circuits capable of operating in high ambient temperatures in the neighborhood of 500 C. or better. With the terminal structure constructed in the above manner it has been determined that resistors embodying the structure are quite rugged, and the number of failures due to breakage of the leads at their point of connection to the resistor is substantially reduced.

An alternative structural arrangement to that illustrated in Figs. 1 and 2, is shown in Fig. 3 of the drawing. In most respects, the alternative arrangement of Fig. 3 is similar to the arrangement of Figs. 1 and 2, however it can be appreciated that the embossment 21 is formed in only one disc 17 of the laminated structure comprising lead cap 16, and the embossment 21 instead of opening on the side of the lead cap opens into its center so that the lead 15 may be led into the center of lead cap 16 and under the embossment 21 in the manner illustrated to form an axial type lead-in terminal structure. In all other respects, the arrangement shown in Fig. 3 is similar to that disclosed in Figs. 1 and 2, and their methods of fabrication are substantially identical.

It is of course possible that the entire laminated structure 16 formed by discs 17 and 18 could have the same embossment formed therein as is formed in disc 17 only, in a manner similar to the arrangement shown in Figs. 1 and 2; however, for simplicity and ease of assembly, embossment of only the disc 17 is adequate for most purposes.

Still another alternative structural arrangement for the new and improved resistor terminal structure is illustrated in Fig. 4 of the drawings. In the embodiment of the structure shown in Fig. 4, all of the elements described with relation to the resistor shown in Figs. 1 and 3 are present; however, in Fig. 4 the metal disc 17 comprising part of each laminated lead cap 16 is formed in the shape of a cup which may be fitted over the end of the ceramic body 11. In all other respects the Fig. 4 arrangement is the same as the resistor shown in Fig. 3. In fabricating the terminal structure of Fig. 4, the cup-shaped disc member 17 serves to hold all of the parts of the terminal structure in assembled relation on the ceramic body 11 to facilitate its further construction. Otherwise, the method of fabrication of the structure shown in Fig. 4 is identical to that of the resistor shown in Fig. 1.

From the foregoing description, it can be appreciated that the invention provides a new and improved termi nal construction for high temperature resistors connecting the resistors to other electrical components capable of operating in ambient temperatures of 500 C. or better, and that the resulting terminal construction is quite reliable while functioning in such ambient temperatures.

Obviously, other modifications and variations of the present invention are possible in the light of the above teachings. t is therefore to be understood that changes can be made in the particular embodiments of the invention described which are within the full intended scope of the invention as defined by the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A high temperature ambient resistor comprising a hollow open ended ceramic body having a coating on the interior surface thereof forming a predetermined electrical resistance between the ends thereof, metal end caps for sealing the open ends of the ceramic body, metal leads for connecting the resistor thus formed in electrical circuit relationship, and metal lead caps alloyed to the end caps and to the leads, the lead caps having an embossment therein for receiving and sealing the ends of the leads, said end caps and said lead caps each comprising a pair of discs, one of said discs consisting essentially of a metal selected from the group consisting of titanium, zirconium, hafnium, thorium,

' tantalum and alloys of these elements with one another and the other of said discs consisting essentially of a metal selected from the group consisting of copper, nickel, iron, molybdenum, chromium, platinum, cobalt and alloys of these elements with one another. 4

2. The resistor set forth in claim 1 wherein the end caps and lead caps are each formed by laminate discs of titanium and nickel bonded at their interface by a titanium nickel alloy, and the leads are formed of platinum wire.

3. A high temperature ambient resistor comprising a hollow open ended ceramic body having a coating on the interior surface thereof forming a predetermined electrical resistance between the ends thereof, metal end caps for sealing the open ends of the ceramic body, metal leads for connecting the resistor thus formed in electrical circuit relationship, and cup-shaped metal lead caps alloyed to the end caps and to the leads, the lead caps having an embossment therein for receiving and sealing the ends of the leads, said end caps and said lead caps each comprising a pair of discs, one of said discs consisting essentially of a metal selected from the group consisting of titanium, zirconium, hafnium, thorium, tantalum, and alloys of these elements with one another and the other of said discs consisting essentially of a metal selected from the group consisting of copper, nickel, iron, molybdenum, chromium, platinum, cobalt, and alloys of these elements with one another.

4. The resistor set forth in claim 3 wherein the end caps and cup-shaped lead caps are each formed by laminate discs of titanium and nickel, respectively, and the leads are formed of platinum wire.

References Cited in the file of this patent UNITED STATES PATENTS 1,835,582 Allen Dec. 8, 1931 2,163,409 Pulfrich June 20, 1939 2,682,595 Rubenstein June 29, 1954 2,786,925 Kahan Mar. 26, 1957 2,803,729 Kohring Aug. 20, 1957 2,857,663 Beggs Oct. 28, 1958 2,901,721 Aronson et a1. Aug. 25, 1959 FOREIGN PATENTS 181,368 Great Britain June 21, 1923 596,436 Great Britain Jan. 5, 1948 OTHER REFERENCES Constitution of Binary Alloys, Hansen, 2nd ed, McGraw-Hill, 1958. Pages 523, 553, 563, 566, 721, 812 and 1046 and others of importance. 

